U.S. patent number 7,541,004 [Application Number 10/987,874] was granted by the patent office on 2009-06-02 for mems-based sensor for lubricant analysis.
This patent grant is currently assigned to Predict, Inc.. Invention is credited to James D. Fousek, Andrew J. Niksa.
United States Patent |
7,541,004 |
Niksa , et al. |
June 2, 2009 |
MEMS-based sensor for lubricant analysis
Abstract
A fluid contamination analyzer employs one or more MEMS-based
sensors. The sensors are incorporated into probes or alternatively
may be employed in an in-line analyzer residing in the fluid. The
sensors, which can be selective to detect a distinct contaminant
within the fluid, sense an impedance of the fluid, which is a
function of its contamination and communicates the impedance to
analysis circuitry.
Inventors: |
Niksa; Andrew J. (Chardon,
OH), Fousek; James D. (Brecksville, OH) |
Assignee: |
Predict, Inc. (Cleveland,
OH)
|
Family
ID: |
36386873 |
Appl.
No.: |
10/987,874 |
Filed: |
November 12, 2004 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20060105467 A1 |
May 18, 2006 |
|
Current U.S.
Class: |
422/82.02;
324/698; 436/150 |
Current CPC
Class: |
G01N
27/126 (20130101) |
Current International
Class: |
G01N
27/00 (20060101); G01N 25/08 (20060101); G01R
27/08 (20060101) |
Field of
Search: |
;422/82.01,82.02
;436/150 ;324/698 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Iotech Catalog, p. 65, Jan. 1995. cited by other .
"Model 958PF On-Line Ferrograph", Foxboro Analytical, 1980, 4 pgs.
cited by other .
"958PF Series On-Line Ferrograph Installation and Operation", The
Foxboro Company, 1980, 6 pgs. cited by other .
"Journal Reprints", The British Institute of Non-Destructive
Testing, M.H. Jones and A.R. Massoudi, Insight, vol. 37, No. 8,
Aug. 1995, pp. 606-610. cited by other .
"Basics of Measuring the Dielectric Properties of Materials",
Hewlett Packard, 1992. cited by other .
"The NIST 60-Millimeter Diameter Cylindrical Cavity Resonator:
Performance Evaluation for Permittivity Measurements", Eric J.
Vanzura, Richard G. Geyer and Michael D. Janezic, Aug. 1993,
National Institute for Standards and Technology Technical Note.
cited by other .
"Advancement of PREDICT/DLI Industrial Sensors", M.A.
Cheiky-Zelina, R.W. Brown and D.E. Schuele, Department of Physics,
Case Western Reserve University, Mar. 1997. cited by other.
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Primary Examiner: Alexander; Lyle A.
Assistant Examiner: White; Dennis M
Attorney, Agent or Firm: Ryan Kromholz & Manion S.C.
Claims
What is claimed is:
1. A fluid contamination analyzer, comprising: a reference
MEMS-based sensor disposed within a reference housing, said
reference housing containing a substantially contaminant-free
volume of the fluid being analyzed; and a plurality of sample
MEMS-based sensors disposed adjacent the reference housing within a
fluid; wherein the reference sensor and the sample sensors further
comprise: a substrate; a plurality of electrodes formed over the
substrate; and a contaminant selective layer disposed adjacent at
least one of (i) the electrodes or (ii) the substrate, said layer
being selective to attract a predetermined contaminant within the
fluid; wherein when a fluid contacts the sensor an impedance of the
fluid may be determined using the electrodes of the sensor, thereby
providing an indication of fluid contamination; a plate electrode
disposed over the reference sensor and at least one sample sensor
of the plurality of sample sensors, wherein when a fluid is
disposed between the plate electrode and the MEMS based sensors an
impedance of the fluid is determined using the plate electrode and
at least one electrode of the MEMS based sensors; associated with
each sensor, a first switch operatively coupled to a first
electrode of the plurality of electrodes; a second switch
operatively coupled to a second electrode of the plurality of
electrodes; a third switch operatively coupled to the plate
electrode; and a fourth switch operatively coupled to the first
electrode and the second electrode wherein the plurality of
switches selectively configure the fluid contamination analyzer to
measure an impedance between the plate electrode and at least one
electrode of the at least one MEMS based sensor or between and
adjacent to the electrodes of the MEMS based sensor.
2. The fluid contamination analyzer according to claim 1, wherein
the contaminant selective layer comprises a top layer disposed over
the electrodes.
3. The fluid contamination analyzer according to claim 2, wherein
the contaminant selective layer is a low-K dielectric material.
4. The fluid contamination analyzer according to claim 3, wherein
the low-K dielectric material is chosen from the group consisting
of nanopourous silica, hydrogensilsesquioxanes, teflon-AF
(Polytetrafluoethylene) and Silicon Oxyflouride.
5. The fluid contamination analyzer according to claim 1, wherein
the electrodes are formed from the group consisting of tungsten,
platinum, gold, chrome, aluminum, polysilicon, titanium, nickel,
copper and silver.
6. The fluid contamination analyzer according to claim 1, wherein
the plurality of electrodes are interdigitated.
7. The fluid contamination analyzer according to claim 6, wherein a
spacing between adjacent electrodes is between about 1 micron to
about 250 microns.
8. The fluid contamination analyzer according to claim 6, wherein a
spacing between adjacent electrodes is less than 1 micron.
9. The fluid contamination analyzer according to claim 1, further
comprising at least one temperature sensor for measuring a
temperature of the fluid in contact with the reference sensor
and/or sample sensors.
10. The fluid contamination analyzer according to claim 9, wherein
the temperature of the fluid is used to compensate the impedance
measurement of the fluid.
11. The fluid contamination analyzer according to claim 9, wherein
the temperature sensor is selected from the group consisting of a
thermocouple, a thermistor and a resistance temperature detector
(RTD).
12. The fluid contamination analyzer according to claim 9, wherein
temperature data and/or sensor data is communicated to a remote
monitoring device through a communications link.
13. The fluid contamination analyzer according to claim 12, wherein
the communications link is a wireless communications link.
14. The fluid contamination analyzer according to claim 1, further
comprising a non-volatile memory module for storing data.
15. The fluid contamination analyzer of according to claim 14,
wherein the data stored in the non-volatile memory module is at
least one of a customer name, a serial number of the sensor, a
manufacture date of the sensor, a calibration factor of the sensor,
a temperature of the fluid, a sensor type, a location of sensor, a
maintenance date of the sensor, a selected reference oil, or an
impedance of the fluid.
16. The fluid contamination analyzer according to claim 14, wherein
the non-volatile memory module is an electrically erasable
programmable read only memory module (EEPROM).
17. The fluid contamination analyzer according to claim 1, further
comprising a temperature sensor for measuring a temperature of the
fluid in contact with the sensor and a non-volatile memory module
for storing data.
18. The fluid contamination analyzer according to claim 1, wherein
the plurality of switches are MEMS switches.
19. The fluid contamination analyzer according to claim 1, wherein
the plurality of switches are formed on the substrate of the MEMS
based sensor.
20. The fluid contamination analyzer according to claim 1, wherein
the plate electrode and the plurality of electrodes are formed from
the group consisting of tungsten, platinum, gold, chrome, aluminum,
polysilicon, titanium, nickel, copper and silver.
21. The fluid contamination analyzer according to claim 1, wherein
the plate electrode is about 1 micron to about 10,000 microns
thick.
22. The fluid contamination analyzer according to claim 1, wherein
the plate electrode is substantially parallel to a top surface of
the at least one MEMS based sensor.
23. The fluid contamination analyzer of claim 1, wherein the
substrate is at least one of a glass substrate or a quartz
substrate.
24. The fluid contamination analyzer of claim 1, wherein the
plurality of electrodes have a width between about 1 micron to
about 50 microns.
25. The fluid contamination analyzer of claim 1, further comprising
a selectively activatable electromagnet in proximity to the sample
sensors, wherein the magnet may be activated and deactivated in
response to control signals and provides a magnet gradient across
the sample sensors, wherein the magnet gradient provides a
contaminant distribution across the sample sensors.
26. A method of analyzing the quality of a sample fluid, wherein
the fluid acts as a dielectric on the sensor, comprising the steps
of: immersing a sample sensor of claim 1 in the sample fluid;
immersing a reference sensor of claim 1 in a substantially
contaminant-free reference fluid, wherein the reference fluid and
the sample fluid are the same type of fluid; measuring an impedance
of the fluid near the surface of the sample sensor and the
reference sensor; and correlating the quality of the sample fluid
to the measured impedance of the sample fluid and the reference
fluid.
27. The method of claim 26, wherein the step of measuring an
impedance includes the step of measuring at least one of
capacitance, resistance, reactance, dissipation factor, phase
angle, admittance, susceptance or conductance.
Description
FIELD OF THE INVENTION
The present invention relates generally to an apparatus and method
for analyzing fluids such as lubricants. More particularly, the
invention relates to a miniature sensor using
micro-electromechanical (MEMS) device technology for detecting and
monitoring conditions of a fluid, such as water content, oxidation
and metallic or conductive particle contamination.
BACKGROUND OF THE INVENTION
The presence of corrosive products, contaminants, metallic
particles, oxidation, etc. in fluids, such as lubricants, can cause
problems. For example, contaminants in lubricants can lead to
damage of machinery in which the lubricant is utilized, causing
unnecessary or accelerated wear on the lubricated members.
Various approaches have been developed to detect conditions
involving deterioration and/or contaminants in fluids. One
conventional system described in U.S. Pat. No. 4,646,070 utilizes a
pair of capacitor electrodes positioned in a fluid. The fluid
serves as a dielectric between the electrodes to develop a
frequency voltage signal across the capacitor electrodes. Based on
such signal, the dielectric, and therefore, the deterioration of
the fluid is determined. However, this solution suffers from a
drawback in that the sensor is large and bulky and is difficult to
move from machine to machine to make fluid contamination
measurements.
U.S. Pat. No. 5,262,732 describes a system, which utilizes an
oscillator circuit coupled to a capacitive sensor. The fluid under
test is placed in a reservoir containing the capacitive sensor. The
oscillator circuit generates a signal having a frequency that
increases or decreases depending on the capacitance of the sensor.
The system of U.S. Pat. No. 5,262,732 is also rather large and
cumbersome and does not lend itself to portability. In the field,
it would be difficult to transport the device from machine to
machine to analyze the lubricant at the location of the machinery,
for example.
Some prior art sensors have been rather large so that a user could
insert the sensor into the fluid and thereby remove a fluid sample
from a machine for analysis. This large, sturdy construction also
allowed the sensor to be subsequently cleaned for use at another
machine without causing damage to the sensor. Unfortunately, in
some machines, obtaining a manual fluid sample with a large,
unwieldy sensor is inconvenient due to machine construction. Also,
in some applications, it is desirable to affix a lubricant analysis
sensor to the machine in the lubricant fluid flow path (called an
in-line configuration) in order that a user may merely attend the
machine and obtain a lubricant contamination reading without having
to insert an analyzer apparatus into the fluid flow path. In some
cases, prior art sensors are too large and unwieldy and do not
conveniently affix to the machine without interfering with proper
machine operation.
As disclosed in U.S. Pat. Nos. 4,047,814 and 5,504,573, magnetic
field gradients have been utilized to precipitate conductive or
ferromagnetic particulates out of a sample fluid (e.g., a
lubricant) such that particulates of varying sizes are withdrawn
along a horizontal strip for subsequent analysis. Knowledge of the
particulate size distribution is then utilized to determine the
status of machinery wear and the potential for failures from
wearing parts, etc. Prior to U.S. Pat. Nos. 4,047,814 and
5,504,573, this method relied upon a visual analysis of particulate
distribution, which was a strong function of the technician's
experience performing the analysis, thereby leading to inconsistent
conclusions. In addition, since the horizontal strip was removed
for analysis, evaluation of the fluid at the machine site was
difficult and, in many cases, impossible.
U.S. Pat. Nos. 4,047,814 and 5,504,573 provided analysis
improvement over the manual analysis by illuminating the
particulate distribution with radiation and detecting the radiation
via a plurality of photodetectors that traverse the particulate
sample. Although such a technique provides for an improvement in
subsequent analysis conclusions, this technique does not overcome
the requirement that an operator initially procure the sample and
send it off-site for analysis. The sample must still be removed for
analysis which limits the locations in which such analysis
materials may be located and, in some cases, prohibits their use
altogether. Further, if one wishes to affix the particulate
distribution collection apparatus with its analysis equipment so
that the horizontal strip need not be removed from the machine, the
radiation source and photodetectors are undesirably large and
thereby further limit the scope of their application.
A miniature sensor for lubricant analysis was disclosed in commonly
owned U.S. Pat. No. 6,204,656. The sensor included one or more
micro-miniature sensors that provided a substantial reduction in
sensor dimensions relative to prior art sensors. The sensors are
incorporated into probes for easy lubricant fluid accessibility or
in an in-line configuration. The sensors sense a capacitance of the
fluid (therefore the impedance), and based on the impedance,
determine the condition of the fluid. The sensor disclosed in U.S.
Pat. No. 6,204,656, however, determined the impedance of the fluid
based on the magnitude of the impedance and contaminant selective
materials were not thoroughly discussed.
In view of the aforementioned shortcomings associated with existing
systems for analyzing conditions of a fluid such as a lubricant,
there is a strong need in the art for a fluid screening device
which provides detailed information regarding the particular types
of contamination, degree of oxidation or other deterioration, etc.
Moreover, there is a strong need in the art for such a screening
device which is miniature and thereby provides for ease of
lubricant contamination status procurement for machine predictive
maintenance programs.
SUMMARY OF THE INVENTION
According to one aspect of the invention, a fluid contamination
analyzer includes at least one sensor. The at least one sensor
includes: a substrate; a plurality of electrodes formed over the
substrate; and a contaminant selective layer disposed adjacent at
least one of (i) the electrodes and (ii) the substrate, said layer
being selective to attract a predetermined contaminant within the
fluid; wherein when a fluid contacts the sensor an impedance of the
fluid may be determined using the electrodes of the sensor, thereby
providing an indication of fluid contamination.
Another aspect of the invention relates to an in-line fluid
contamination analyzer, including: an array of MEMS-based sensors
located within a fluid, wherein each sensor includes a substrate, a
plurality of electrodes formed over the substrate, and a
contaminant-selective layer disposed adjacent the electrodes, said
array including: a first MEMS-based sensor having a first
contaminant-selective layer which is selective to attract a first
class of contaminant within the fluid; a second MEMS-based sensor
having a second contaminant-selective layer which is selective to
attract a second class of contaminant within the fluid; and a third
MEMS-based sensor having a third contaminant-selective layer which
is selective to attract a third class of contaminant within the
fluid; wherein each sensor is operative to determine an impedance
of the fluid contacting each sensor, thereby providing an
indication of fluid contamination.
Yet another aspect of the invention relates to a fluid
contamination analyzer, including: a first reference MEMS-based
sensor disposed within a reference housing, said reference housing
containing a substantially contaminant-free volume of the fluid
being analyzed; and a plurality of sample MEMS-based sensors
disposed adjacent the reference housing within a fluid.
Another aspect of the invention relates to a fluid contamination
analyzer, including at least one MEMS-based sensor, said at least
one sensor including: a substrate; a plurality of conductors formed
over the substrate; and a local heater disposed adjacent the at
least one MEMS-based sensor, said local heater providing a
temperature gradient through which the fluid is run; wherein the
conductors form electrodes of the sensor and when a fluid contacts
the sensor an impedance of the fluid may be determined as a
function of temperature, thereby providing an indication of fluid
contamination.
Yet another aspect of the invention relates to a method of
analyzing the quality of a fluid, including the steps of: immersing
a sensor into the fluid, wherein the fluid acts as a dielectric for
the sensor; obtaining a complex impedance of the fluid; measuring a
temperature of the fluid in contact with the sensor; applying a
correction factor to the complex impedance based on the measured
temperature of the fluid; and estimating the quality of the fluid
based on a comparison of known fluids producing substantially the
same Dissipation Factor and complex impedance values.
Another aspect of the invention relates to a method of analyzing
the quality of a fluid, including the steps of: immersing a sensor
into the fluid, wherein the fluid acts as a dielectric for the
sensor; measuring an impedance of the fluid over a temperature
gradient; and estimating the quality of the fluid based on a change
in slope of the measured impedance over the temperature
gradient.
Yet another aspect of the invention relates to a method of
analyzing the quality of a fluid in which a sensor has been
immersed, wherein the fluid acts as a dielectric on the sensor,
including the steps of: using a contaminant selective layer on the
sensor to selectively attract contaminants within the fluid near a
surface of the sensor; measuring an impedance of the fluid near the
surface of the sensor; and correlating the quality of the fluid to
the measured impedance of the fluid.
Another aspect of the invention relates to a method of analyzing
the quality of a sample fluid, wherein the fluid acts as a
dielectric on the sensor, comprising the steps of: immersing a
sample sensor in the sample fluid; immersing a reference sensor in
a substantially contaminant-free reference fluid, wherein the
reference fluid and the sample fluid are the same type of fluid;
measuring an impedance of the fluid near the surface of the sample
sensor and the reference sensor; and correlating the quality of the
sample fluid to the measured impedance of the sample fluid and the
reference fluid.
Other aspects, features, and advantages of the invention will
become apparent from the following detailed description. It should
be understood, however, that the detailed description and specific
examples, while indicating several embodiments of the present
invention, are given by way of illustration only and various
modifications may naturally be performed without deviating from the
present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1A is a top view of a MEMS-based sensor according to an
embodiment of the invention.
FIG. 1B is a cross section diagram illustrating the field of view
of the MEMS-based sensor of FIG. 1A
FIG. 2A is a cross section diagram illustrating the MEMS-based
sensor of FIG. 1A taken along arrows 2A-2A.
FIG. 2B is a cross section diagram illustrating an alternative
MEMS-based sensor according to the invention.
FIG. 2C is a cross section diagram illustrating another alternative
MEMS-based sensor according to the invention.
FIG. 3A is a diagram illustrating use of the MEMS-based sensor of
FIG. 1A in an elongate probe.
FIG. 3B is a diagram illustrating use of the MEMS-based sensor in a
rigid, elongate probe having a handle.
FIG. 3C is a diagram illustrating a MEMS-based sensor array at one
end of a probe.
FIG. 4 is a top view illustrating an array of MEMS-based sensors as
disclosed in FIG. 1A.
FIG. 5 is a side view of a system according to one aspect of the
invention having an array of MEMS-based sensors placed within a
magnetic field intensity gradient.
FIG. 6 is a top view of an alternative embodiment of the invention,
wherein an array of MEMS-based sensors have variations in electrode
spacings.
FIG. 7 is a top schematic view of an alternative embodiment of the
invention, wherein an array of MEMS-based sensors includes a
reference sensor.
FIG. 8 is a sectional view illustrating an array of MEMS-based
sensors including a reference sensor, wherein the MEMS based
sensors are mounted on a probe.
FIG. 9A is a top view of an alternative embodiment of the
invention, wherein an array of MEMS-based sensors include a
selective layer to detect particular contaminants, wherein the
selective layer is formed between the electrodes and the
substrate.
FIG. 9B is a top view of an alternative embodiment of the
invention, wherein an array of MEMS-based sensors are selective to
detect particular contaminants, wherein the selective layer is
formed over the electrodes and the substrate.
FIG. 9C is a top view of an alternative embodiment of the
invention, wherein an array of MEMS-based sensors are selective to
detect particular contaminants, wherein each substrate is formed of
a different selective material.
FIG. 10 is a perspective view of an in-line fluid analyzer having
an array of MEMS-based sensors in a lubricant fluid flow path
having both circuitry for analyzing the impedance and communicating
the results to other circuitry.
FIG. 11 is a top view of an alternative embodiment of the
invention, wherein a local heater is employed to generate a
temperature gradient.
FIG. 12 is a top view of an alternative embodiment of the
invention, wherein the MEMS based sensor includes a temperature
sensor.
FIG. 13 is a top view of an alternative embodiment of the
invention, wherein the MEMS based sensor includes a non-volatile
memory device.
FIG. 14 is a side view of an alternative embodiment of the
invention, wherein the sensor includes a MEMS based sensor and a
plate electrode.
FIG. 15 is a block, system level diagram illustrating an
environmental view of the invention, wherein a plurality of
machines contain MEMS-based sensors for sensing fluid contamination
and circuitry for communicating the results to a central data
analysis and storage site.
FIG. 16 is a flow diagram illustrating an exemplary method of
estimating the quality of a fluid in accordance with an embodiment
of the present invention.
FIG. 17 is an exemplary database structure used to store fluid
sample data in accordance with an embodiment of the present
invention
DETAILED DESCRIPTION OF THE INVENTION
The present invention will now be described with reference to the
drawings wherein like reference numerals are used to refer to like
elements throughout. As will become more apparent based on the
following description, a fluid contamination analyzer for
monitoring contaminants in lubricating fluids utilizes
micro-electromechanical (MEMS)-based sensors, thereby substantially
reducing the sensor dimensions while providing a similar electrical
response. This results in a greater variety of machine fluid
analysis applications for the sensor. The MEMS-based sensor
fabrication techniques also allow for a substantial reduction in
sensor costs and provide high sensor manufacturability. Such
fabrication techniques also allow for a substantial number of
sensor variations with a sensor array for collecting a variety of
types of data relating to fluid contamination.
Throughout the disclosure, reference will be made to impedance and
impedance measurements. Impedance can be represented and analyzed
in many forms, and each are contemplated to fall within the scope
of the present invention. For example, impedance may be
characterized as capacitance, complex capacitance, resistance and
reactance, capacitance and dissipation factor, impedance and phase
angle, admittance, susceptance and conductance. Each of these
characterizations have their own terminologies. For example, for
capacitance the terms capacitance, dissipation factor, Tan delta, Q
factor or loss factor may be utilized.
Additionally, the invention will be described with respect to an
in-line sensor. However, the sensor can be applied in other
configurations and/or applications, and the description with
respect to an in-line sensor is not intended to be limiting in any
way. Other configurations include, for example, placement of the
sensor in a sump (e.g., not in a direct path of fluid flow) or
external from the fluid flow (e.g., a separate test unit not part
of the machine).
FIG. 1A is a top view of a MEMS-based sensor 10 formed using MEMS
device fabrication techniques. The sensor 10 includes a substrate
12, preferably made of glass or quartz, upon which a conductive
layer is formed and etched to create a pair of interdigitated
conductors 14 and 16, respectively. The first conductor 14 forms a
first electrode 14 while the second conductor 16 forms a second
electrode 16. The electrodes are interdigitated to provide
uniformity in impedance measurement. Alternatively, the electrodes
may take on any suitable configuration and still fall within the
scope of the invention. The electrodes 14, 16 can be less than 1
micron wide, the limiting factor being the ability to manufacture
the thin electrodes and the conductivity of the material. There is
no particular constraint on the upper limit of the electrode width.
In one embodiment, the electrodes have a width between about 1
micron and about 50 microns.
In another embodiment, the substrate 12 can be made of ceramic or a
semiconductor material, such as silicon, silicon nitride, silicon
carbide, germanium and the like. As is discussed more fully below,
the substrate material may be chosen to provide an optimized
selectivity with respect to one or more contaminants being
detected.
In yet another embodiment, the interdigitated electrodes 14, 16 are
formed of tungsten, platinum, gold, chrome, aluminum, polysilicon,
titanium, nickel, copper, silver, and the like. Electrodes 14 and
16 are electrically isolated from one another and may be coupled to
either discrete instrumentation or circuits integrated with the
substrate 12 or other integrated circuits via bond pads 18 and 20,
respectively. Since the sensor 10 is fabricated using conventional
MEMS-based and/or semiconductor processing techniques, fine line
width geometries may be constructed thereby allowing the sensor
dimensions to be 1 mm by 1 mm or smaller. MEMS-based techniques
allow the sensor to be reduced in size while maintaining a
relatively large feedback signal and, therefore, achieving good
precision of the measured data.
During operation, the sensor analyzes a thin film of material,
e.g., a fluid, directly adjacent to the sensor surface. In other
words, an electric field of the sensor 10 extends up into the fluid
at least a distance equal to about the line spacing 17 (i.e., the
distance of separation between adjacent electrodes) of the
electrodes 14, 16 and generally a distance significantly further.
For example, and with further reference to FIG. 1B, if the line
spacing 17 were 10 microns, then the sensor 10 could analyze or
"look into" the fluid 2 a distance 4 of at least 10 microns above
the surface of the sensor 10. Similarly, if the line spacing were
100 microns, then the sensor 10 could analyze the fluid at least
100 microns above the surface of the sensor 10. The line spacing 17
of the electrodes 14, 16 can be less than 1 micron or up to about
250 microns, for example. In one embodiment, the line spacing of
the electrodes 14, 16 is 1 micron wide and equally spaced (e.g.,
the line spacing 17 is 1 micron), and in another embodiment the
line spacing is about 2 microns and equally spaced. As will be
appreciated, the line spacing 17 may be larger or smaller as
desired.
The sensor 10 operates in the following manner. When the sensor 10
comes into contact with a fluid sample, the fluid acts as a
dielectric between the electrodes 14, 16 thereby impacting the
impedance of the sensor. By way of example, the sensor can be
approximated by a parallel plate capacitor having a capacitance
characterized by C=.di-elect cons.A/d, wherein A is the electrode
surface area and d represents the electrode spacing. The measured
capacitance provides an indication of the properties of the
dielectric (the fluid). Accordingly, the sensor 10 senses the
capacitance (and therefore the impedance) of the fluid at its leads
(bond pads 18 and 20) and provides this value at the bond pads 18
and 20 for analysis by analysis circuitry (not shown). The analysis
circuitry takes the impedance value and determines the level of
fluid contamination based upon a comparison with 1) a known clean
fluid sample; 2) an expected or reference value; or 3) by trending,
e.g., looking at a change over time of a capacitance, a phase
angle, resistance, dielectric, etc. Various methods exist for
analyzing fluid contamination. At least one method contemplated by
the present invention includes using the sensed fluid impedance as
a component within an oscillator circuit, thereby impacting the
circuit's oscillating frequency which may be used to determine the
level of fluid contamination. This method is disclosed in detail in
co-owned U.S. Pat. No. 6,028,433 entitled "Portable Fluid Screening
Device and Method," which is hereby incorporated by reference in
its entirety.
It is to be appreciated that impedance is generally measured.
Therefore, the term sensor "impedance" will be used in the
remainder of this disclosure. It should be noted that although the
capacitance of the fluid is analyzed through the impedance, the
impedance sensor 10 extends to other fluid impedance variations and
therefore, for example, contemplates inductive type sensors within
the scope of the present invention.
Turning now to FIG. 2A, a cross sectional view of the sensor 10
taken along lines 2A-2A of FIG. 1A is illustrated. The sensor 10
has the electrodes 14 and 16 located along a horizontal plane on
the substrate 12. When a lubricant fluid sample contacts the sensor
10, it rests between and/or above the electrodes 14 and 16, thereby
affecting the dielectric constant therebetween. Accordingly, the
presence of contaminants within the fluid results in different
impedance readings of the sensor at its leads (bond pads 18 and
20). These differences are analyzed via analysis circuitry (not
shown) to determine, within an acceptable accuracy bandwidth, the
level of fluid contamination, which may then be used, for example,
either as an indication for timely fluid replacement or an
indication of machine wear for preventative maintenance and/or
quality control purposes.
Although the electrodes 14 and 16 are illustrated in FIG. 2A as
residing entirely within a single horizontal plane, it should be
understood that the substrate 12 may undertake a variety of
contours and the electrodes 14 and 16 may follow that contour to be
customized for various applications as may be desired. Each of
these sensor variations are contemplated by the present invention.
In an alternate embodiment, illustrated in FIG. 2B, the sensor 22
includes insulating layer 21, such as silicon nitride, between the
substrate 12 and the electrodes 14 and 16. As is described more
fully below, the insulating layer 22 serves a variety of purposes,
including, but not limited to, electrically insulating the
electrodes 14 and 16 from an electrically conductive substrate 12,
providing a sensor that can operate at higher operating
temperatures, and enhancing selectivity of the sensor with respect
to detecting a particular contaminant within the fluid under
test.
FIG. 2C is a cross-sectional view of an alternative embodiment of a
sensor 23 similar to the sensor 10 of FIG. 1A. Sensor 23 includes
the substrate 12 having the electrodes 14 and 16 formed thereon.
Subsequently, an insulating layer 24, such as silicon dioxide
layer, is formed over the electrodes 14 and 16 which helps protect
the sensor 23 from experiencing "shorts" across the electrodes 14
and 16 caused, for example, by substantially sized conductive
particulates in a fluid under test. The insulated sensor 23
provides improved performance in detection of non-particulate forms
of contamination, for example, water content in the fluid or fluid
oxidation. Additionally, and as will be described in more detail
below, the insulation layer 24 can be selected to enhance the
selectivity of the sensor with respect to detecting a particular
contaminant within the fluid under test or to prevent accumulation
of soils or contaminants on the sensor surface.
As stated above, the sensors 10, 22 and 23 of FIGS. 2A, 2B and 2C
substantially reduce the dimensions of a fluid sensor from
approximately 2 in..times.2 in. to approximately 1 mm.times.1 mm,
thereby providing substantial improvements in procuring fluid
samples for analysis. For example, a probe utilizing a sensor
having such dimensions may easily be inserted into a machine
containing a fluid for analysis without either substantially
impacting the machine's operation or requiring any disassembly of
the machine. FIG. 3A illustrates a probe assembly 30 incorporating
the sensor at one end 31. The bond pads 18 and 20 (not shown) of
the sensor 10 are coupled to lines 32 and 34 along a flexible probe
body 36, thereby transmitting the fluid impedance sensed by the
sensor 10 to an analysis circuit 38. The flexible, elongate probe
body 36 allows a user to manipulate the probe into numerous shapes
to access difficult-to-reach fluid samples within operating
machinery. Further, since the sensor 10 is compact in size, the
sensor 10 does not negatively impact the size of the probe 30 at
the end 31, thereby facilitating the testing of fluid samples in
difficult-to-reach locations without adversely impacting a
machine's operation or requiring a disassembly of the machine.
In FIG. 3A, the analysis circuitry 38 is illustrated as being
separate from the probe. Alternatively, the analysis circuitry may
reside at the end 31 of the probe 30 as a circuit integrated with
the sensor 10. This alternative embodiment advantageously provides
for fluid contamination level determinations to be made local to
the measurement site itself, thereby improving analysis accuracy by
eliminating errors due to electrical line losses and noise.
FIG. 3B, much like FIG. 3A, is a diagram illustrating an
alternative probe assembly 40 having a sensor 10 at one end 41. The
sensor 10 is connected to lines 32 and 34 via bond pads 18 and 20
(not shown), which extend through a substantially rigid channel
member 42 to a handle 44. The handle 44 provides for ease of use
and connects the lines 32 and 34 to the analysis circuitry 38.
Alternatively, handle 44 may contain a communications circuit
therein to provide wireless transmission of the fluid impedance
data to the analysis circuitry 38 through an RF data link, for
example. Such wireless capability provides even greater flexibility
by allowing a user to be unimpeded by any wire length, etc., which
is useful and safe in a factory setting utilizing heavy machinery
having moving parts. Although the rigid channel member 42 is not as
ductile as the elongate body 36 of FIG. 2A, the channel member 42
provides for firm, precise positional control of the sensor
location, while the handle 44 allows a user to easily manipulate
the probe assembly 40 while avoiding hazards present by moving
parts within the machinery.
Another advantage provided by the dimensional feature of the sensor
10 is that an array of such sensors may be incorporated together
within a single probe assembly without substantially impacting the
probe size. FIG. 3C illustrates such a probe assembly 50 wherein an
array 52 of sensors reside at one end 53 of the probe assembly 50.
It is to be appreciated that FIG. 3C greatly exaggerates the
dimensions of the array 52 with respect to the other members in
order to illustrate the array 52 of sensors 10. In actual practice,
the sensor array 52 can reside at the end 53 of the probe assembly
50 and not be substantially larger than the channel member 42, for
example. In one embodiment, the sensor array 52 may be utilized to
provide improved analysis accuracy by providing impedance
measurement redundancy. For example, since a fluid contamination
concentration is not always uniform (such as when a substantially
large particulate is identified, which skews the aggregate
contamination determination), the sensor array 52 allows for
multiple fluid impedance readings to be collected and subsequent
data processing techniques used to interpret the data to accurately
determine the fluid contamination level. For example, multiple
readings may be averaged together or if one reading is
substantially different from the others, it may be ignored.
Alternatively, various statistical operations may be performed on
the collected data to yield a more accurate determination of fluid
contamination. When utilizing an array 52 as illustrated in FIG.
3C, each sensor 10 at the probe end 53 may be individually
hard-wired to analysis circuitry 38 via the channel member 42 and
handle 44. Alternatively, a time multiplexer circuit (or other type
multiplexing methodology) may be utilized at the end 53 of the
probe assembly 50 to reduce the need for multiple lines 32 and 34
in the channel member 42 to thereby keep the probe assembly 50
compact.
The sensor array 52 of FIG. 3C may comprise various configurations.
In one embodiment, multiple sensors 10 may be formed on a single
substrate 12, such as the array 60 illustrated in FIG. 4. In one
embodiment, multiplexing circuitry may be integrated onto the
substrate 12 to collect the multiple measured fluid impedances and
multiplex them (via either time multiplexing or other multiplexing
technique) for transmission via lines 32 and 34 to the analysis
circuitry 38. Further still, the analysis circuitry 38 may also be
integrated onto the substrate 12 such that data acquisition and
fluid contamination determination may be made at the end 53 of the
probe assembly 50, thereby reducing fluid determination errors due
to line loss, noise, etc. Alternatively, multiple discrete sensors
10 having separate substrates 12 may reside on another support
structure and be affixed to the end 53 of the probe assembly
50.
The sensor arrays 52 and 60 of FIGS. 3C and 4 may comprise various
array configurations as may be desired. For example, as
illustrated, the sensor array 52 may be configured in a
longitudinal row or be stacked vertically. In addition, the sensor
array 52 may extend into two dimensions to form a square shaped
sensor or any type of pattern depending upon the desired
application. In yet another alternative embodiment, the sensor
array may extend into three dimensions by stacking the sensors
above one another such that sufficient space is provided for fluid
contact to the various sensors. Any configuration of sensors 10 to
form one dimensional, two dimensional or three dimensional arrays
are contemplated by the present invention.
FIG. 5 is a system level diagram which illustrates a fluid
contamination analyzer system 90 having a substrate 92 upon which a
sensor array 94 resides, wherein each sensor 95 is constructed and
behaves as the sensors 10, 22 and 23 of FIGS. 2A, 2B and 2C,
respectively. Each sensor 95 is coupled (not shown) to the analysis
circuitry 38 either directly or via a multiplexer circuit that may
reside on the substrate 92. A magnetic field source 96, preferably
an electromagnet coil or a movable permanent magnet, is coupled to
a magnetic control circuit 98 to selectively activate the magnetic
field source 96, such that the magnetic field may be turned on and
off as desired. The magnetic field source 96 is preferably oriented
to provide a magnetic field intensity gradient along a length of
the sensor array 94. Preferably, the orientation is determined by a
spacer wedge 100, as illustrated, however, other mechanisms such as
brackets, etc. may also be utilized and are contemplated by the
present invention.
The sensor array 94 of FIG. 5 operates in the following manner. A
lubricant fluid for analysis is brought into contact with the
sensor array 94. This may be accomplished by either placing the
fluid contamination analyzer system 90 on a probe and inserting the
sensor array 94 into the fluid or preferably affixing the system 90
to a machine in the fluid flow path to thereby provide an in-line
fluid analyzer. In another embodiment, the fluid may be removed
from the machine and brought into contact with the sensor array 94.
The magnetic control circuit 98 activates the coil 96, thereby
generating a magnetic field. The sensor array 94, due to its
positional orientation with respect to the coil 96, experiences a
magnetic field intensity gradient along its length such that at one
end a large magnetic field intensity (H.sub.1) is experienced at
the substrate 92, while at another end a substantially smaller
magnetic field intensity (H.sub.2) is experienced at the substrate
92. Due to the magnetic field intensity gradient, ferromagnetic
particles (contaminants) of differing sizes in the fluid are
distilled from the fluid flow path onto the sensor array 94, such
that a particulate distribution is generated across the sensor
array 94. Therefore, each sensor 95 in the sensor array 94 will
have a unique impedance due to the size and quantity of the
particulates at that location. This impedance information is then
used by the associated analysis circuitry 38 and processors to
determine how much contamination exists at differing particulate
sizes, which may be utilized to determine wear modes, wear trends,
etc. After the impedance data has been collected, the magnetic
control circuit 98 deactivates the coil 96 or moves the permanent
magnet away, thereby turning the magnetic field off. Without any
magnetic field acting on the particles, the force of fluid flow
substantially removes particles from the sensor array 94.
Various modifications and alternative embodiments may be employed
with the sensor array 94. In one alternative embodiment, a magnetic
field intensity gradient may be achieved by utilizing a plurality
of independent magnetic field sources fixed at varying distances
from the substrate 92 or wherein each source has a unique magnetic
field intensity such that their aggregation provides a magnetic
field intensity gradient. Any type of magnetic field source or
configuration of sources that would provide a variable magnetic
field intensity across the sensor array 94 is contemplated in the
present invention. Furthermore, although a coil is the preferred
magnetic field source 96, any other type of magnetic source falls
within the scope of the present invention.
Another embodiment is illustrated in FIG. 6. FIG. 6 is a top view
of a sensor array 110 wherein a substrate 12 contains a plurality
of sensors 10 formed thereon. Each sensor 10 is much like the
sensor of FIG. 1A (or alternatively sensors 22 or 23 of FIGS. 2B
and 2C), having a substrate 12, conductors (electrodes) 14 and 16
and bond pads 18 and 20. The sensor array 110 differs from the
sensor array 60 of FIG. 4 in that at least one of the sensors
varies from the others with respect to the spacing between the
interdigitated electrodes. For example, as illustrated in FIG. 6,
sensor 10a has a somewhat close conductor spacing (d.sub.1) for
fine-sized particulates, sensor 10b has a larger electrode spacing
(d.sub.2) for medium-sized particulates and sensor 10c has a
relatively larger electrode spacing (d.sub.3) to accommodate
large-sized particulates (wherein d.sub.1<d.sub.2<d.sub.3).
Such a variable electrode spacing sensor array 110 further
accommodates particulate contamination distribution determinations
by helping to delineate the size of the particulates due to the
difference in spacing of the electrodes 14 and 16. Therefore to
carry out this feature, the sensor 10c is preferably located within
the array 110 near the largest magnetic field intensity which has
sufficient strength to distill large-sized contaminants from the
fluid, while sensor 10a preferably is located within the array 110
near the weakest magnetic field intensity which has sufficient
strength to distill small-sized contaminants from the fluid.
With reference now to FIG. 7, a sensor array 210 includes a
substrate 12 and a plurality of sensors 10a, 10b, 10c formed
thereon. Each sensor includes a substrate 12, a pair of electrodes
14 and 16 and associated bond pads 18 and 20. In one embodiment, a
first sensor 10a serves as a reference sensor, while the other
sensors 10b, 10c are sample sensors for detecting one or more fluid
contaminants, including, but not limited to, particles, water,
acid, and the like.
In one embodiment, illustrated in FIG. 8, a sensor assembly 212
includes the sensor array 210 and a sensor housing 217. As shown,
the reference sensor 10a is exposed or otherwise subjected to a
known reference fluid 19, within the reference housing 13, having a
composition and purity, which remains relatively fixed. For
example, in a machine which employs a lubrication or cooling oil
(flowing in a direction along arrows 215), the reference sensor 10a
may be contained or otherwise housed in a reference housing 13,
which is disposed adjacent the sample sensors 10b, 10c. In one
embodiment, the reference housing 13 is comprised of a thermally
conductive material, such that the temperature of the reference
fluid 19 within the reference housing 13 is at approximately the
same temperature as the fluid circulating throughout the
machine.
Preferably, the reference sensor 10a is immersed in or otherwise
exposed to "clean" oil, i.e., oil which is not circulated
throughout the machine and is not readily exposed to contamination.
In this embodiment, the reference sensor is exposed to a reference
oil having the same composition as the oil circulated throughout
the machine. In addition, the reference oil and associated
reference sensor 10a are subjected to all of the same conditions as
the circulated oil and associated sample sensors 10b, 10c, except
for the contaminants which develop in the circulated oil over time.
As such, the capacitance readings from sample sensors 10b, 10c can
be compared to the capacitance reading from reference sensor 10a in
order to determine changes (e.g., the development and or presence
of contaminants) in the circulated sample oil, and thereby
providing enhanced accuracy. It is to be appreciated that the
sensor assembly 212 of FIG. 8 may be used in conjunction with a
probe, such as those illustrated in FIGS. 3A-3C, as well as in an
in-line configuration (as illustrated in FIG. 13). It is to be
appreciated that the reference housing 13 may be removable in order
for the reference fluid 19 contained therein to be changed
periodically.
With reference to FIG. 9A and continued reference to FIGS. 1-4, in
another alternative embodiment, a sensor array 310 includes a
substrate 12 and a plurality of sensors 10a', 10b', 10c' formed
thereon. Preferably, each sensor 10a', 10b', 10c' is sensitive to
or otherwise selective of a particular fluid contaminant. More
particularly, each sensor 10a', 10b', 10c' can include a different
contaminant-selective layer. For example, the contaminant-selective
layer can include an insulating or intermediate layer 21a, 21b,
21c, disposed between the electrodes 14, 16 and the substrate 12,
as shown in FIG. 2B. Each intermediate layer 21a, 21b, 21c is
chosen in order to provide a surface to which a fluid containing a
contaminant of interest would preferentially adhere, thereby
providing a stronger impedance measurement of the presence of the
particular contaminant of interest within the fluid.
For example, an intermediate layer comprised of glass would be
particularly sensitive to water within the fluid, while an
intermediate layer comprised of silicon nitride would be
particularly sensitive to soot and oxidation within the fluid. The
sensitivity of a particular contaminant selective layer with
respect to a particular contaminant can be determined empirically.
The contaminant selective layer can be formed from silicon nitride,
silicon dioxide, cerium dioxide, glass, quartz, aluminum oxide,
aluminum nitride, boron nitride, titanium nitride, gallium nitride,
diamond, diamond like carbon and silicon carbide. Hydrophilic
materials provide more sensitivity to water, while hydrophobic
materials provide less sensitivity to water.
According to one embodiment, the contaminant selective layer is
formed from organic coatings, such as parylene, epoxy, polyimide,
polycarbonate, polyester, polyphenylene sulfide, and the like.
According to another embodiment, the contaminant selective layer is
formed from a low-K material or stack of materials to form a low-K
dielectric stack. As used herein, a "low-K material" or a "low-K
dielectric material" refers to a material, or stack of materials,
having a relative permittivity in one embodiment of about 5 or
less, and in another embodiment of about 3 or less. Relative
permittivity is the ratio of the absolute permittivity (.di-elect
cons.) found by measuring capacitance of the material to the
permittivity of free space (.di-elect cons..sub.o), that is
K=.di-elect cons./.di-elect cons..sub.o.
Examples of low-K dielectric materials include nanopourous silica,
hydrogensilsesquioxanes, teflon-AF (Polytetrafluoethylene), Silicon
Oxyflouride and the like. It is noted that above-identified low-K
materials are not an exhaustive list of low-K materials and other
low-K materials may be available.
In an alternative embodiment of FIG. 9B, one or more of the sensors
10a'', 10b'', 10c'' in the sensor array 210, 310 may be covered
with an insulating film or layer, as illustrated in FIG. 2C, to
provide non-particulate contamination information, such as the
water content of the fluid and/or fluid oxidation for analysis.
Again, each insulating film 24a, 24b, 24c is chosen in order to
provide a surface to which a fluid containing a contaminant of
interest would preferentially adhere, thereby providing a stronger
capacitive measurement of the presence of the particular
contaminant of interest within the fluid. For example, an
insulating film comprised of glass would be particularly sensitive
to water within the fluid, while an insulating film comprised of
silicon nitride would be particularly sensitive to soot and
oxidation within the fluid.
In yet another alternative embodiment shown in FIG. 9C, each sensor
is formed on a substrate 12a, 12b, 12c, of different material,
which is selective of or otherwise sensitive to a particular
contaminant being detected. In this embodiment, each sensor
substrate 12a, 12b, 12c, may be mounted to a common base structure
such that the sensors are disposed in proximity to one another. For
example, a substrate comprised of glass would be particularly
sensitive to water within the fluid, while a substrate comprised of
silicon nitride would be particularly sensitive to soot and
oxidation within the fluid.
FIG. 10 is a perspective view of the sensor system 130 in an
in-line configuration in which the sensors 10 themselves are in a
fluid flow path 132 of a machine. As discussed supra, the sensor 10
senses the fluid impedance and transmits this data to the analysis
circuit 38, which analyzes and/or processes the data to arrive at a
fluid contamination determination. This result may then be
communicated either visually to a user who is taking a fluid
contamination reading via a display (not shown) or may
alternatively communicate the result to a central data collection
station (not shown) via the communications control circuit 128
which is operable to transmit data, preferably via an RF signal, to
the data collection station.
With reference now to FIG. 11, a sensor system 410 in accordance
with an alternative embodiment is illustrated. The system includes
one or more sensors 10 disposed adjacent a local heater 412, which
is controlled by a heater control 414. A local heater, as used
herein, refers to a heater that is within about 5 to about 1000
microns from the sensor. The actual location of the heater with
respect to the sensor is not critical, and the heater need only
cause a change in temperature of the fluid so a temperature slope
can be determined. The sensor system 410 performs impedance
measurements on a fluid sample as the fluid is run through a
temperature gradient. In one embodiment, the sensor system 410 is
integrated into a probe assembly, such as is illustrated in FIGS.
3A-3C. Alternatively, the probe system 410 is embodied in an
in-line configuration, such as is illustrated in FIG. 10. Because
the rate at which the sensed impedance changes with temperature
(temperature slope) is altered by contamination of the fluid, the
change in slope can be used as an indication of fluid condition. It
is to be appreciated that this embodiment of the invention may be
employed in conjunction with a single sensor system as well as a
multi-sensor array.
Referring now to FIG. 12, an alternative embodiment of the sensor
420 is illustrated. The sensor 420 is similar to the sensor 10, 22,
23 shown in FIGS. 2A-2C, and includes electrodes 14,16 located
along a horizontal plane on the substrate 12. When a lubricant
fluid sample contacts the sensor 10, it rests between and above the
electrodes 14 and 16, thereby affecting the dielectric constant
therebetween. Accordingly, the presence of contaminants within the
fluid results in different impedance readings of the sensor at its
leads (bond pads 18 and 20). Bond pads 18, 20 provide a connection
point for coupling to discrete instrumentation or circuits
integrated with the substrate. Additionally, the sensor 420
includes a temperature sensor 422, such as, for example, a
thermocouple, a thermistor, or a Resistance Temperature Detector
(RTD). Terminals 424, 426 provide a connection means for connecting
the temperature sensor 422 to a monitoring device, such as the
analysis circuitry 38 (FIG. 3A), for example. As will be
appreciated, the number of terminals required for the temperature
sensor 422 depends on the type of temperature sensor implemented,
e.g., two terminals for a thermocouple, three terminals for a
3-wire RTD, etc. Alternatively, the temperature data from the
temperature sensor 422 and fluid data from the sensor may be
transmitted to the analysis circuitry 38 wirelessly or through a
data communications link. The temperature sensor 422 provides a
temperature measurement of the fluid that is in contact with the
sensor 420. The temperature measurement can be used by the analysis
circuitry to improve the accuracy of the analysis of the fluid,
e.g., by compensating the impedance measurement of the fluid based
on the temperature of the fluid.
For example, correction factors can be applied to the data obtained
by the sensor 420 based on the temperature of the fluid. It may be
known that the sensor 420 produces a first set of data for a fluid
in a first temperature range, and a second set of data, which is
different from the first set of data, in a second temperature
range. In each case the fluid is identical (except for
temperature), yet different test data is obtained. To compensate
for this difference, a correction factor can be applied to the
measured data based on the measured temperature of the fluid. It
should be appreciated that the correction factor can be applied by
the analysis circuitry 38 or by the temperature sensor 422 itself.
Alternatively, temperature data obtained from the temperature
sensor 422 can be used for monitoring the fluid temperature,
thereby eliminating the need for a separate temperature sensor.
With reference now to FIG. 13, another embodiment of the sensor is
illustrated. The sensor 430 again is similar to the sensor of FIGS.
2A-2C, and includes electrodes 14,16 located along a horizontal
plane on the substrate 12. Bond pads 18, 20 provide a connection
point for coupling to discrete instrumentation or circuits
integrated with the substrate, as described previously.
Additionally, the sensor 430 includes a non-volatile memory module
432, such as an EEPROM. The non-volatile memory module 432 is
operatively coupled to the sensor to receive data, such as sensor
data, temperature data, etc. Additionally, the non-volatile memory
module is operatively coupled to a memory controller (not shown).
Memory controllers are well known and therefore will not be
discussed in detail. Briefly, the memory controller coordinates the
data routed to the non-volatile memory module 432 and the data
retrieved from the non-volatile memory module. Additionally, the
memory controller instructs the non-volatile memory module to store
and/or to retrieve data to/from non-volatile memory.
The non-volatile memory module 432 can store and/or retrieve data
pertaining to the sensor, e.g., calibration data, date of
manufacture, serial number, sensor type etc., customer data, e.g.,
customer name, location, etc., or application data, e.g., location
of the sensor, last maintenance date of the sensor, selected
reference fluid (e.g., reference oil), operating time, minimum and
maximum operating temperature, minimum and maximum fluid
measurements (e.g., impedance, temperature), etc. As will be
appreciated, numerous other types of data can be stored in the
non-volatile memory module 432 as required. Additionally, the
temperature sensor 422 of the sensor 420 and the non-volatile
memory module 432 of the sensor 430 can be combined in a single
sensor, thereby providing both memory storage/retrieval functions
and temperature monitoring functions on a single sensor.
With reference to FIG. 14, another embodiment of the sensor is
illustrated. The sensor 440 includes a MEMS based sensor 442 as
described in any one of the previously discussed embodiments. The
MEMS based sensor 442 includes electrodes 14,16 located along a
horizontal plane on the substrate 12. Bond pads (not shown) provide
a connection point for coupling to discrete instrumentation or
circuits integrated with the substrate. Above the MEMS sensor 442
is a plate electrode 444, which can be formed from any one of
several materials, including, for example, tungsten, platinum,
gold, chrome, aluminum, polysilicon, titanium, nickel, copper,
silver and the like. The plate electrode 444 is generally
rectangular in shape, although it should be appreciated that other
shapes can be implemented without departing from the scope of the
invention. The plate electrode 444 has a footprint that is about
equal to a footprint of the MEMS based sensor 442. Additionally,
the plate electrode 444 is generally parallel to the MEMS based
sensor 442. The plate electrode can be less than 1 micron to about
10,000 microns thick, and the spacing 446 between the plate
electrode and a top surface 448 of the electrodes 14, 16 can range
from 50 to about 3000 microns. In one embodiment, the spacing 446
is about 1000 microns.
A first connector 450 couples the first electrode 14 to analysis
circuitry 38 via a first switch 452. A second connector 454 couples
the second electrode 16 to the analysis circuitry 38 via a second
switch 456. A third connector 458 couples the plate electrode 444
to the analysis circuitry 38 via a third switch 460. A fourth
connector 462 and a fifth connector 464 couple the first electrode
14 to the second electrode 16 via a fourth switch 466. Finally, a
fifth connector 468 couples the plate electrode 444 to an
electrostatic field control circuit 470 via a fifth switch 472.
As will be appreciated, the above described switches can be MEMS
based switches or any other suitable switch used in low power
signal systems. Additionally, connections for operating the
switches are not shown. Such connections, however, would be obvious
to one skilled in the art and therefore are omitted for sake of
brevity. The switches can be located remote from the sensor 440,
e.g., in or near the analysis circuitry 38, or integrated on the
sensor 440, e.g., on the substrate 12 of the MEMS based switch 442.
Based on the switch settings, the sensor 440 can operate in anyone
of several modes.
In a first mode, the first switch 452 and the second switch 456 are
closed, while the third switch 460 and the fourth switch 466 are
open. In this mode of operation, the sensor 440 behaves as the
sensors previously described herein, i.e., the sensor analyzes the
fluid between and above the electrodes 14, 16 within its field of
view. The sensor 440 is immersed in a fluid and a measurement is
made by the analysis circuitry 38 via the first and second
connectors 450, 454. The fluid surrounding the electrodes 14, 16 of
the sensor 440 acts as a dielectric between the electrodes 14, 16
thereby impacting the impedance of the sensor. The analysis
circuitry 38 determines the level of fluid contamination based upon
either a comparison with a known clean fluid sample or with an
expected or reference value.
In a second mode, the first switch 452 and the third switch 460 are
closed, and the second switch 456 and the fourth switch 466 are
open. In this configuration the sensor 440 measures the impedance
of the bulk fluid between the first electrode 14 and the plate
electrode 444. The first electrode 14 and the plate electrode 444
form the respective plates of a parallel plate capacitor, and the
fluid between the plates forms the dielectric material. The
analysis circuitry 38 determines the level of fluid contamination
based upon either a comparison with a known clean fluid sample or
with an expected or reference value.
In a third mode, the second switch 456 and the third switch 460 are
closed, and the first switch 452 and the fourth switch 466 are
open. In this configuration the sensor 440 measures the impedance
of the bulk fluid between the second electrode 16 and the plate
electrode 444. The second electrode 16 and the plate electrode 444
form the respective plates of a parallel plate capacitor, and the
fluid between the plates forms the dielectric material. The
analysis circuitry 38 determines the level of fluid contamination
based upon either a comparison with a known clean fluid sample or
with an expected or reference value.
In a fourth mode, the first switch 452, the third switch 460 and
the fourth switch 466 are closed, and the second switch 456 is
open. In this configuration the sensor 440 measures the impedance
of the bulk fluid between the combination of the first electrode 14
and the second electrode 16 and the plate electrode 444. The first
electrode 14 and the second electrode 16 form a first plate of a
parallel plate capacitor, and the plate electrode 444 forms the
second plate of a parallel plate capacitor. The fluid between the
two plates forms the dielectric material. The analysis circuitry 38
determines the level of fluid contamination based upon either a
comparison with a known clean fluid sample or with an expected or
reference value. It is noted that the same configuration can be
obtained by opening the first switch 452 and closing the second,
third and fourth switches 456, 460, 466.
In a fifth mode, the first switch 452, the second switch 456 and
the fifth switch 472 are closed and the third switch 460 and the
fourth switch 466 are open. The sensor 440 operates in the
following manner. After a magnetic field source (not shown) is
deactivated, particulates are preferably washed away due to fluid
flow. There are frequently, however, particulates that contain a
residual static charge large enough to remain stuck to one of the
electrodes 14 and 16 despite the fluid flow over the electrodes.
The electrostatic field control circuit 470 then applies a voltage
to the plate electrode 444 such that an electrostatic field is
generated that is sufficiently large such that particulates are
dislodged and washed away by the fluid flow. In this manner, fluid
contamination accuracy is improved by eliminating the chance of
residual particulates from previous fluid sample measurements
interfering with subsequent fluid measurements by washing performed
periodically via the electrostatic control circuit 470 and the
plate electrode 444.
FIG. 15 is a system level diagram, which illustrates a dynamic
fluid contamination analysis system 500. System 500 includes a
central data collection, processing and storage unit 502, which
contains a processor 504, an RF communications circuit 506 and a
memory 508. The central data collection unit 502 may also include
an I/O port, an input peripheral device and a display for
interacting with a user. The system 500 includes a plurality of
machines 510, 512, 514, 516 and 518 which operate in a factory
setting and utilize fluids of lubricant and cooling purposes. Each
machine contains a sensor system 130 (as illustrated in FIG. 10,
for example) that performs in an in-line configuration.
Periodically, as dictated by the processor 504 and RF
communications circuit 506, the sensor systems 130 are instructed
to measure the fluid impedance of the fluid in their respective
machines. Each sensor system 130 then communicates its present
fluid impedance to the processor 504 via its communications control
circuit 128. The processor 504 then makes a fluid contamination
determination, stores it in the memory 508 for trending purposes
and indicates the determination to monitoring personnel if the
fluid contamination level exceeds a predetermined threshold. In
this manner, the fluid contamination analysis system 500 monitors a
plurality of machines without requiring a user to go from machine
to machine taking fluid samples and interfering with the machine
operation. In addition, since the sensor arrays of the present
invention are small, they may serve in in-line configurations
without interfering with machine operation.
With reference to FIG. 16, a flow diagram of an example technique,
or process 600 of determining the quality of a fluid in accordance
with the present invention is illustrated. The process 600 can be
thought of as depicting steps in a method. The flow diagram
includes a number of process blocks arranged in a particular order.
As should be appreciated, many alternatives and equivalents to the
illustrated process 600 may exist and such alternatives and
equivalents are intended to fall within the scope of the claims
appended hereto. Alternatives may involve carrying out additional
steps or actions not specifically recited and/or shown, carrying
out steps or actions in a different order from that recited and/or
shown, and/or omitting recited and/or shown steps. Alternatives
also include carrying out steps or actions concurrently or with
partial concurrence.
As will be described more fully below, the method includes
immersing a sensor into a fluid and measuring the impedance of the
sensor and fluid. Based on the measured impedance, the quality of
the fluid is estimated.
The method will be described in conjunction with the analysis
circuitry 38 previously discussed herein. In the exemplary
embodiment, the analysis circuitry is the computer 500 (FIG. 15)
executing program instructions that carry out the steps of the
method. It should be appreciated that the particular vehicle used
to implement the method is not germane to the invention, and other
forms of the analysis circuitry are contemplated. For example, the
analysis circuitry could be configured as a group of discrete
components interconnected together to form a logical circuit.
The sensor of the present invention can be modeled as a resistor
having a resistance R connected in parallel with a capacitor having
a capacitance C. Thus, the sensor includes both real and reactive
components.
Another factor for consideration is the dissipation factor (DF). DF
represents one form of heat-producing losses within a capacitor. DF
and "loss tangent" are largely equivalent terms describing
capacitor dielectric losses. DF refers specifically to losses
encountered at low frequencies. At high frequencies, capacitor
dielectric losses are described in terms of loss tangent (tan
.delta.). The higher the loss tangent, the greater the capacitor's
equivalent series resistance (ESR) to signal power.
For small and moderate capacitor values, losses within the
capacitor occur primarily in the dielectric, the medium for the
energy transfer and storage. The dielectric loss angle, .delta., is
the difference between (theta) and 90.degree.. The name "loss
tangent" simply indicates that tan .delta. goes to zero as the
losses go to zero. Note that the dielectric's DF is also the
tangent of the dielectric loss angle. These terms are used
interchangeably in the art.
The actual values of R and C for the sensor model as well as the DF
are dependent on the sensor itself as well as on the fluid the
sensor is measuring. A clean or new fluid will produce values of R,
C and DF that are distinct from values of R, C and DF produced by a
contaminated or used fluid. Based on the measured values of R, C,
and DF, the analysis circuitry can estimate the remaining life of
the fluid, the particular type of contamination in the fluid, e.g.,
water, metal, soot, oxidation, additive depletion, etc., and the
relative amounts of the particular type of contamination in the
fluid.
Beginning at step 602, a sensor in accordance with the present
invention is immersed in a fluid, such as oil from an internal
combustion engine, for example. At step 604, the processor 504
initializes a counter, and at step 606 the processor selects an
initial frequency f1. The selected frequency f1 can range between
0.1 Hz and 10 MHz, and preferably is at an optimum frequency for
the application. According to one embodiment, f1 is between about
100 Hz and 20 KHz. The processor 504 applies the selected frequency
to the bond pads 16, 18 of the sensor at step 608, and the
temperature and impedance of the sensor/fluid are measured by the
processor.
Moving to step 612, the processor 504 stores the measured
temperature and impedance in memory 508 for use in later steps. At
step 614, the processor checks the counter to determine if another
iteration is required. If the counter is less than or equal to n,
then at step 616 the processor 504 increments the counter, and at
step 618 the processor selects a second test where electrical
conditions may be changed in frequency, voltage, time duration or
not changed as required by the test protocol for the application.
For example, the frequency f2 can be higher, lower or equal to the
frequency f1. Preferably, the frequency f2 is about 10 times the
frequency f1 of the previous iteration. After selecting the second
frequency, the processor 504 moves back to step 608, and the
process is repeated for n tests as required by the protocol for
that application.
Moving back to step 614, if the processor 504 determines the
counter is greater than n, then at step 620 the processor retrieves
the measured data from memory 508. At step 620, the processor
calculates functions that best represent the oil conditions of
concern, e.g., the impedance at each frequency. Threshold values
for the functions will be determined with used fluids with known
levels of contamination and/or depletion. Processor 504 will
generate a report of the test point, date/time, multiple test
functional values for the test point, threshold functional values
and temperature, for example.
For example, and as was noted previously, the sensor can be modeled
as a resistor connected in parallel to a capacitor. The impedance
can be measured by applying a sine wave signal of a given frequency
and amplitude to the sensor and comparing the input signal to the
output signal with respect to amplitude and phase shift (phase
angle). From this information, and using the parallel R-C
(resistor-capacitor) model of the sensor, the impedance is resolved
into real and reactive components.
Moving to step 622, once the impedance is resolved into its real
and reactive components, a correction factor is applied to the
complex impedance. The correction factor is based on the measured
temperature of the sample fluid during the impedance measurement
relative to the measured temperature of a reference fluid during
its impedance measurement. The correction factor can be a simple
fraction, an equation describing the change in impedance as
temperature varies, or a lookup table containing the impedance of a
stable fluid at various temperatures. According to one embodiment,
temperature compensation factors are generated for a particular
reference fluid type after all measurements of the reference fluid
have been made at various temperatures.
As was discussed previously, impedance measurements of certain
fluids can be affected by the temperature of the fluid. Impedances
may increase, decrease or remain unchanged throughout a temperature
range. Due to the operating characteristics of a particular
machine, it may not be feasible to obtain an impedance measurement
of a sample fluid at the same or similar temperature as an
impedance measurement of a reference fluid. In such situations, a
correction of the measured impedance of the sample fluid provides
increased accuracy of the impedance measurement and, thus,
increased accuracy in the estimate of the condition of the fluid.
The correction factor for a given fluid can be stored in memory,
such as a database, which is discussed in more detail below.
Now that a corrected value of the complex impedance has been
calculated, the processor at step 624 retrieves reference fluid
data from memory (e.g., data stored in a reference database on a
storage medium, such as a hard drive of a computer). Referring
briefly to FIG. 17, an exemplary database structure 700 that can be
used to construct the reference database is illustrated. The
database structure 700 includes a reference name entry 702, which
is a listing of fluid names that may be used in a particular
machine or process, e.g., 80 weight gear lube, Brand X 10W-40 motor
oil, etc. A real component of impedance entry 704 stores the real
component of impedance for the particular reference fluid, and a
reactive component impedance entry 706 stores the reactive
component of impedance for the particular reference fluid. A
reference temperature entry 708 stores the temperature of the
reference fluid during its impedance measurement, and a temperature
compensation entry 710 stores the correction factor for the
particular fluid. Additionally, a DF entry 712 stores the
dissipation factor for the fluid and, finally, a fluid property
entry 714 provides information relating to the characteristics of
the particular fluid. For example, the condition of the reference
fluid (e.g., new, used, etc.), the type of contaminants in the
fluid (e.g., soot, water, fuel, etc.) and/or the amount of
contaminant in the fluid (e.g., 1% fuel) is entered in the fluid
property entry 714.
As will be appreciated, multiple columns for fluid property can be
included in the database structure 700 depending on the
requirements of the system. For example, a first fluid property
entry can be dedicated to the age or remaining life of the fluid, a
second fluid property entry can be dedicated to the type of
contaminant in the fluid, and a third fluid property entry can be
dedicated to the amount of the contaminant in the fluid.
Additionally, the impedance may be expressed in other terms as
described previously, e.g., terms other than real/reactive
components and DF.
Each reference fluid is entered into the reference database along
with its respective properties as in the above described entries.
For example, a first fluid name entry 702 may be Brand X 10W-30
motor oil, and is entered in a first row 720 of the database.
Corresponding fluid properties, real component of impedance,
reactive component of impedance, reference temperature, correction
factor, and DF also are stored in the first row under their
respective columns. A second fluid name may be the same fluid,
e.g., Brand X 10W-30 motor oil, and is entered in a second row 722
of the reference database, along with its corresponding fluid
properties, real component of impedance, reactive components of
impedance, reference temperature, correction factor and DF. As
should be apparent, the second entry will have a different fluid
property, and thus different values for the real component of
impedance, the reactive component of impedance, or the DF. The
reference temperature entry 708 may or may not be the same,
depending on the temperature of the second reference fluid during
its impedance measurement. The temperature compensation entry 710
is the same for reference fluids of the same type. Further entries
can be made for the same type of fluid and/or for different types
of fluid, as needed. In one embodiment, the reference database
includes a single type of reference fluid, and numerous entries for
the reference fluid at various levels of contamination and/or
various type of contaminants.
In operation, the processor searches and retrieves from the
database 700 fluid name entries 702 that match the fluid sample
being tested. From the list of matching fluid names, the processor
searches the real component of impedance 704, the reactive
component of impedance 706, and the DF 712 for values that match or
are within a specified range of the calculated real component of
impedance, the calculated reactive component of impedance and the
calculated DF for the sample fluid. At step 626, the processor 504
estimates the sample fluid to have the same fluid properties as a
reference fluid of the same type with the same or similar DF, real
component of impedance and reactive component of impedance. At step
628, the status of the fluid is reported to a user via an screen,
e.g., a computer monitor, or via a status indicator, for
example.
The various features of the present invention may be utilized in a
variety of applications, configurations and packages. For example,
the aspects of each embodiment can be mixed and matched to create
alternative embodiments. Each variation is contemplated as falling
within the scope of the present invention. Additionally, the
sensors may be potted or secured in a DIP (dual in-line package)
for easy insertion and replacement. Furthermore, the number of
iterations at various frequencies may be increased as required.
Although the invention has been shown and described with respect to
certain preferred embodiments, it is obvious that equivalents and
modifications will occur to others skilled in the art upon the
reading and understanding of the specification. The present
invention includes all such equivalents and modifications, and is
limited only by the scope of the following claims.
* * * * *